I have had a regular S6 64 GB version since March 30. I came from a Nexus 5. My thoughts are that I'm happy with the device overall. I love the camera, the fingerprint reader, the speed of the device, and the screen. I did see some lag with the Samsung keyboard, but I switched to the Google keyboard and haven't experienced any lag since. I use Nova Prime as my launcher and have had no lag there or any other issues. I am using a Speck candyshell case. While I normally don't like cases, the phone was too slick for me without a case.
There are only two things about the phone that could be improved for me. I have found the bluetooth volume to be rather low. In my truck, I play music over bluetooth and the S6 is noticeably quieter than my Nexus 5 was. My other complaint is just the regular battery life. The battery has been better than my Nexus 5, but that isn't saying much. I just wish they would have made the back of the device flush with the camera (not a fan of camera bumps) and used that newly created space for a bigger battery. Please no attacks or posts informing me about wireless charging or quick charging or changing my settings, etc. - I'm not bashing anything here and I am happy with the phone.
Overall, I'm happy with my decision as this device currently checks off more check boxes on my wishlist than any other device.